The present invention relates to a waveform data analyzer, such as a digital storage oscilloscope or logic data analyzer, and particularly relates to compressing samples and extracting features of a waveform that has a plurality of waveform states.
Waveform data analyzers acquire, process, store and display large amounts of waveform data for analysis and display over extended periods of time. To accommodate requirements for digitizing and analyzing waveforms with greater bandwidths, sample rates of analog-to-digital converters in waveform data analysis systems have increased to tens of gigasamples per second. The large amount of data requiring storage and transfer for display can result in undesirable delays and loss of data. Compression of the waveform samples enables efficient use of resources in the waveform data analysis system, including the memory for storing waveform data and the high-speed data interfaces for transferring waveform data for display. Compression is vital for supporting increasing data bandwidths in waveform data analysis systems.
In the commonly owned U.S. Pat. No. 7,071,852 B1 (“the '852 patent”) entitled “Enhanced Test and Measurement Instruments Using Compression and Decompression,” dated Jul. 4, 2006 and incorporated herein by reference, the present inventor describes compression and decompression of bandlimited signals. Compression and decompression in a digital storage oscilloscope (DSO) are described in the '852 patent with respect to FIGS. 38 and 39. The algorithms disclosed apply to compressing/decompressing bandlimited signals and measuring signal parameters such as the center frequency. In the commonly owned and copending U.S. patent application Ser. No. 11/458,771 (the '771 application) entitled, “Enhanced Time-Interleaved A/D Conversion Using Compression,” filed on Jul. 20, 2006, the present inventor describes compression of a bandlimited signal that is sampled by a parallel time-interleaved analog-to-digital converter (TIADC). The compression methods described therein are designed to take advantage of the parallel architecture of the TIADC. The compression methods of the '771 application can be implemented in a waveform analysis system, such as a DSO, that includes a TIADC. The present invention is directed to compression and decompression of a signal waveform with recurring waveform states and teaches specialized algorithms for this particular type of waveform.
In general, current digital oscilloscopes use a type of data compression that is actually data reduction for rapid display of reduced data. The data compression methods select only certain samples to represent all the waveform samples in a particular time interval. Selection methods described by Holcomb et al. in U.S. Pat. No. 5,790,133 include peak detection, where only the minimum and maximum samples for every N number of samples are selected, and glitch detection, where only the glitch samples for every N number of samples are selected. This type of data compression is actually data reduction, where most samples are simply discarded. The resulting reduced data include only a small fraction of the original samples. Furthermore, this type of compression by reduction is irreversible. Other waveform samples of the N samples cannot be reconstructed from the selected samples. Architectures for these digital oscilloscopes include a deep memory for storing the original waveform samples, allowing zoom-in display functions. The deep memory is continuously rewritten by newly acquired waveform samples.
Digital oscilloscope architectures also include processors that detect properties of the waveform samples. In U.S. Pat. No. 6,989,833 B2, Narita describes processing pulsed waveforms for measurements of pulse width, period, duty cycle, rise time and fall time.
A logic data analyzer architecture that includes data compression is described by Endo et al. in U.S. Pat. No. 7,031,882 B2. For this architecture, probes acquire digital signals that are input to a logic analyzer device where they are compressed by run-length encoding prior to transfer over a high speed interface to a computer. The computer can decompress the compressed data for display or further compress the data for storage.
In US Patent Application 2006/0143518 A1, Cheng et al. describe a logic analyzer device that compresses test data for storage on the device. The compressed data is decompressed before transmission over an interface to a computer where it is displayed. In US Patent Application 2006/0075212A1, Cheng et al. describe a logic analyzer that compresses test data for storage in a memory or a buffer and decompresses the compressed data for display. Neither of these applications describe a compression method.
It is often the case that the waveform being analyzed has two or more waveform states. The waveform states can represent recurring characteristics or redundancies in the waveform. The present invention exploits redundancies in the waveform shape to achieve more efficient compression than is available from conventional methods. Furthermore, the present invention's compression algorithms are computationally efficient so that compression can be performed in real time, or as at least fast as the sample rate of the waveform samples, rather than by post-processing of the waveform samples already stored in an acquisition memory.
The efficiency and speed of compression in the present invention increase the capacities of the resources of the waveform data analysis system, including memory and data transfer interfaces. The waveform data analysis system can store more waveform data and transfer data at a higher speed for further analysis or display to a user.